A phased array is a group of antenna elements in which the relative phases of respective signals feeding the antenna elements are varied to coordinate radiation patterns of the array so that the radio wave signals are reinforced in certain directions and suppressed in others. The relative amplitudes of the signals, as well as the constructive and destructive interference effects among the signals radiated by the individual antenna elements, determine the effective radiation pattern of the array.
A phased array may be used to point a fixed radiation pattern, or to scan rapidly in azimuth or elevation. Transmitters utilizing phased array techniques have been implemented successfully for many years. Common applications for phase arrays include, for example, narrow band military radar systems.
More recently, the capability of phased array techniques has gradually extended to include wide band, multi-signal, multi-polarization military jammers. However, the feed network and support electronics for this type of jammer is complex and contains a large number of individual hardware elements including multiple amplitude adjust modules, time delay modules, phase shift modules, and signal couplers. This is because conventional phased array architectures separate signal generation, beam forming and signal polarization functions.
Most recently, an additional requirement of phased arrays includes the ability to independently steer individual beams for each signal. Adding this capability further increases the system complexity by nearly the number of signal beams. In particular, a phase-locked multi-signal exciter must be coupled to each antenna array element. As such, the system implementation with conventional phased array architectures approaches a practical limit that precludes extending the architecture to more than a hand full of radio wave signals.
Consider, for example, the multiple amplitude adjust modules that are required in a phased array. Conventional multi-signal RF output amplitude control is implemented using “open loop” techniques that require complex factory calibration tables to compensate for known amplitude and phase distortion in the RF power amplifiers associated with each antenna element. Without phase control feedback, the beam steering phase shifters must be complex true time delay (TTD) in order to achieve a wide RF bandwidth. Such an “open loop” approach results in imperfect antenna beam steering, and may also require frequent re-calibration due to system hardware maintenance repair or other changes to the factory-calibrated system.
In addition, conventional RF leveling loops cannot be effectively extended to multi-signal systems. Instead, RF leveling loops provide minimal effectiveness and are used more to protect amplifiers from damage than to optimize RF performance and efficiency. For instance, if there is more than one signal present or a strong interfering signal, a conventional RF leveling loop can level on the wrong signal. This can result in unnecessary power reduction and loss in efficiency. In short, conventional phased array beam forming techniques and RF leveling loop architectures are relatively large, require a substantial number of components, require complex factory calibration, and provide limited RF performance and efficiency.
What is needed, therefore, are phase array techniques and leveling loop architectures that provide enhanced RF performance and efficiency relative to conventional techniques and architectures.